1. Field of the Invention
The invention relates to a rotary roller surface cleaning method and a rotary roller surface cleaning apparatus.
2. Description of Related Art
A rare earth magnet that uses a rare earth element such as a lanthanoid is also called as a permanent magnet, and is employed in a motor for a hard disk or a motor used in MRI, a drive motor for a hybrid vehicle or an electric vehicle, and so on.
Remanent magnetization (remanent magnetic flux density) and coercive force may be cited as indices of a magnet performance of a rare earth magnet. Increases in heat generation due to miniaturization and increased current density in motors have led to increased demand for heat resistance in rare earth magnets used in such motors. In response to this demand, research has been conducted into techniques for maintaining the coercive force of a magnet during use in high temperatures. With respect to an Nd—Fe—B magnet, which is a rare earth magnet frequently used in drive motors for vehicles, attempts have been made to increase the coercive force of the magnet by refining crystal grains, using an alloy with a composition containing a large amount of Nd, adding a heavy rare earth element exhibiting a superior coercive force performance, such as Dy or Tb, and so on.
Rare earth magnets include common sintered magnets in which the crystal grains (main phase) constituting the structure are on a scale of approximately 3 to 5 μm, and nano-crystal magnets in which the crystal grains are refined to a nanoscale of approximately 50 to 300 nm. Among these magnets, attention is currently focused on nanocrystal magnets, in which the required amount of expensive heavy rare earth elements can be reduced while refining the crystal grains.
A method of manufacturing a rare earth magnet can be described briefly as follows. For example, first, a molten metal (an Nd—Fe—B molten metal) of a rare earth magnet material is formed in a furnace, whereupon the molten metal is supplied from the furnace to a rotary roller. The molten metal is then rapidly solidified in order to manufacture a quenched ribbon (a quenched thin strip). Next, the quenched ribbon is cut into a desired size and formed into a magnet powder, whereupon the powder is sintered while being pressure-molded in order to manufacture a sintered body. In the case of a nano-crystal magnet, the sintered body is further subjected to hot plastic processing in order to apply magnetic anisotropy thereto, whereby a molded body is manufactured. A modified alloy constituted by an alloy containing a heavy rare earth element or an alloy not containing a heavy rare earth element, such as an Nd—Cu alloy, is applied to the molded body using one of various methods, whereby a rare earth magnet having an enhanced coercive force performance can be manufactured.
Incidentally, agglutinated material formed when the molten metal agglutinates may adhere to a surface of the rotary roller that quenches the molten metal. Further, irregularities may be formed on the surface of the rotary roller due to corrosion, dents, and so on, and the molten metal supplied from the furnace may be spattered by the agglutinated material and irregularities on the surface of the rotary roller. When the molten metal is spattered, the number of dents and the like on the surface of the rotary roller increases, and agglutinated material is more likely to adhere thereto.
For example, when foreign matter such as agglutinated material adheres to the surface of the rotary roller, the molten metal is not cooled sufficiently in a location where the foreign matter is adhered, and as a result, the quality of the manufactured quenched ribbon may deteriorate.
Hence, a method of stopping rotation of the rotary roller periodically, examining the surface of the rotary roller visually or the like, cleaning the surface when the existence of adhered foreign matter or the like is confirmed by removing the foreign matter, and then restarting rotation of the rotary roller in order to resume manufacture of the quenched ribbon may be employed. With this method, however, the rotary roller needs to be stopped periodically, and therefore the quenched ribbon cannot be manufactured efficiently.
Here, Japanese Patent Application Publication No. 2001-41904 (JP 2001-41904 A) describes a foreign matter removal apparatus that removes silver paste powder adhered to a transparent electrode of a touch panel by pressing a squeegee type pressing member against a surface of the touch panel in order to detect the position of the powder, controlling a linear motor in order to move an X-Y stage holding a CCD camera and a laser apparatus for removing the powder to the position of the powder, capturing an image of the powder using the CCD camera, calculating the precise position of the powder on the basis of the captured image, and then removing the powder using the laser apparatus.
According to this apparatus, the foreign matter can be removed by detecting the precise position of the foreign matter automatically. However, the apparatus described in JP 2001-41904 A is not an apparatus used to detect foreign matter on the surface of a rotating rotary roller and remove the detected foreign matter.